1. Field of the Invention
The present invention relates to an information-inputting device that can record data in a recording medium in real time while the data is being written on a recording surface without specifying types of writing implements and materials used for the recording surface.
2. Description of the Related Art
Methods and apparatuses for inputting information have been proposed, and have been put to practical use. For instance, Japanese Laid-open Patent Application No. 6-289989 discloses an information recognition device. The information recognition device provides a camera on one side of a recording surface. The information recognition device detects coordinates of each position of information recorded by a writing implement on the recording surface, for example, a track of letters written on recording paper, and develops depiction data based on the coordinates. The information recognition device alternatively detects coordinates of each position of a writing implement, that is, coordinates of a tip of the writing implement, and develops depiction data based on the coordinates. To recognize the information recorded on the recording surface, the information recognition device also needs to detect the origin of the coordinates on the recording surface by detecting corners of the recording paper, that is, the recording surface, and the origin of the X-axis and the Y-axis recorded on the recording paper.
The information recognition device must detect the corners of the recording paper or the origin of the coordinates based on the information recorded on the recording paper before detecting the coordinates of each position of the information every time the recording paper is exchanged. Additionally, in a case that a position of the recording paper is moved from its original position while recording the information on the recording paper, or in a case that positions of the corners of the recording paper in an image being taken by the camera are moved, coordinates of recording the information on the recording paper are detected by the camera as different coordinates from what they are supposed to be, since the coordinates of recording the information are calculated based on the origin of the coordinates. Consequently, the camera detects different information from what a user intends to record unless a moved origin of the coordinates is detected.
Additionally, when the camera photographs the information recorded on the recording paper from an upper oblique direction of the recording paper, error between actual coordinates of the information recorded on the recording paper and coordinates detected by the camera increases as a distance between the recording paper and the camera increases. Such a problem will be described with reference to FIGS. 1A and 1B. An angle θ indicates an angle range that a fixed number of pixels provided in the vertical direction of an imaging device such as the camera can detect light through a lens. In FIG. 1A, a distance on the recording paper that the imaging device can detect with the angle θ is a distance L1. In FIG. 1B, a distance on the recording paper that the imaging device can detect with the angle θ is a distance L2. It is assumed that the distance L2 is greater than the distance L1. Accordingly, the greater the distance between the recording paper and the camera, the wider an area on the recording paper that can be detected by the camera with the angle θ. In other words, an area on the recording paper detected by each pixel that is provided in the imaging device increases as the distance between the recording paper and the camera increases. Accordingly, when the camera photographs the information recorded on the recording paper from the upper oblique direction of the recording paper, the error between the actual coordinates of the information recorded on the recording paper and the coordinates detected by the camera increases as the distance between the recording paper and the camera increases. Thus, an image detected by the camera is contracted with respect to an image corresponding to the information recorded on the recording paper.
The number of pixels provided in the imaging device necessary for obtaining image data by photographing the coordinates of each position of the information depends on a size of a recording area on the recording paper and a resolution of reading the coordinates of each position of the information recorded on the recording paper. As the size of the recording area increases, the greater the number of pixels necessary for calculating the coordinates from the image data also increases. Additionally, for a higher resolution of reading the coordinates, the number of pixels must be greater. Furthermore, a frame rate of image signals outputted from the imaging device must be high in order to clearly monitor an information recording process from the photographed image data. However, an imaging device with a large number of pixels and a high frame rate is generally expensive, and thus it is hard to hold down production cost of an information input device by mounting such an imaging device thereon. Consequently, a writing input device with a comparatively inexpensive imaging device using a smaller number of pixels has been requested.
Additionally, a size of an image-display device used in a portable writing input device for displaying the image data obtained by the camera is preferred to be small for miniaturization of the device and its electric efficiency. However, if the size of the image-display device is small, the number of pixels displayed on the image-display device becomes small, and thus quality of the image data displayed on the image-display device decreases by stretching the image data immoderately when displaying a page of the image data thereon. Furthermore, when the number of imaging devices used for photographing the information recorded on the recording paper is small, a wide-angle lens should be attached to each of the imaging devices for photographing the information. In such case, a resolution of reading the coordinates of the information recorded on the recording paper differs depending on where the information is recorded on the recording paper.